1. Field of the Invention
Apparatuses consistent with the present invention relate to a weighing system using the principle of electromagnetic force compensation.
An exemplary weighing system compatible with the invention includes a permanent magnet system with an air gap and a shielding cover. A coil disposed in the air gap of the permanent magnet system produces the load-dependent counterforce. A transmission lever has a longer lever arm to which the coil is attached and a shorter lever arm on which the weight transferred by a load receiver acts either directly or is reduced through additional levers. A position sensor which detects the position of the transmission lever is arranged near the coil. A control amplifier is used to control the current flowing through the coil.
2. Description of the Related Art
Related art weighing systems are disclosed, for example, in German Publication DE 37 43 073 A1.
When these weighing systems have high dead loads on the load receiver, e.g., heavy weighing pans or roller conveyors, which may also be equipped with motors to drive the rollers, these dead loads must either be compensated by additional current in the coil, which generates additional heat, or counterweights are attached to the transmission lever. A weighing system with a counterweight is disclosed, for example, in the German Publication DE 198 04 439 C1. Here, the transmission lever is extended beyond the fixation point of the coil and carries the counterweight at the end of the lever. This solution is suitable only for slow weighings, however. Natural oscillations of the transmission lever, which have nodal points on the lever bearing and on the counterweight, interfere with rapid weighings. These oscillations are excited by the forces of the coil, which change rapidly in rapid weighings and subside only slowly, such that the time to reach a stable weighing result is relatively long.